This invention relates to a method of binding lignocellulosic materials utilizing ammonium based spent sulfite liquor as the thermosetting adhesive binder.
The most commonly used adhesive binders for binding wood products are urea-formaldehyde and phenol-formaldehyde, with the more expensive phenol-formaldehyde being used for exterior grade products. Using these conventional binders, the cost of the binder itself accounts for a large portion of the total material cost of the wood product.
There have been numerous proposals for utilizing spent sulfite liquor, the by-product of the sulfite pulping process, as an adhesive binder. In U.S. Pat. No. 2,822,358 to Hearon, Lackey and Martin, there is described a process of chemical modification of ammonium based spent sulftie liquor by heat under controlled conditions. The converted liquor is proposed for a variety of water soluble products including adhesives, dispersants and surface active agents. U.S. Pat. No. 3,141,873 to Goss involves heat treating of ammonium based spent sulfite liquor and reacting the treated liquor with a crosslinking agent such as acetone or formaldehyde to produce a thermosetting binder for making cellulosic board. U.S. Pat. No. 2,786,008 to Henschler describes a method of mixing ammonium based spent sulfite liquor with phenol formaldehyde resin and used the resulting mixture as adhesive for fiberboard and plywood. Most of the prior proposals involve extensive chemical modification of the spent sulfite liquor before use as a binder and the cost for producing these modified binders is not significantly lower than conventional adhesives. Moreover, few of these modified binders can produce exterior grade products.
In U.S. patent application No. 898,671 by K. C. Shen, is described a composition in which spent sulfite liquor is treated with sulfuric acid. Although an exterior grade product can be produced by this method at costs less than conventional adhesives the acid treatment complicates the system. In the acid treated spent sulfite liquor it is believed that the sulfuric acid generates free lignosulfonic acid. Under the heat and pressure of the hot pressing operation, the lignosulfonic acid condenses and polymerizes into an insoluble state similar to the condensation reaction of conventional thermosetting resin binders.